In recent years, active research aimed at commercialization of organic EL devices has been conducted. Organic EL devices can achieve high current densities at low voltages, and so are expected to make possible high emission brightnesses and high emission efficiencies, and in particular, the commercialization of organic multicolor EL displays capable of high-definition multicolor or full-color display is expected. One example of methods to achieve multicolor or full-color display of organic EL displays is a method in which a plurality of types of color filters which transmit light in specific wavelength regions (color filter method) are used. When applying the color filter method, the organic EL device used is required to emit, as multicolored light, so-called “white light”, which contains light in three primary colors (red (R), green (G), and blue (B)) in a good balance.
In order to obtain a multicolor-emission organic EL device, the following, and similar, are being studied:
(a) methods of using an emission layer containing a plurality of light-emitting dyes, and simultaneously exciting the plurality of emitting dyes (see Japanese Patent Publication No. 2991450 and Japanese Patent Application Laid-open No. 2000-243563);
(b) methods of using an emission layer containing a host emission material and a guest emission material, exciting the host emission material and causing emission, and simultaneously moving energy to the guest material, causing the guest material to emit light (see U.S. Pat. No. 5,683,823, Specification);
(c) methods of using a plurality of emission layers containing different emitting dyes, and exciting the emitting dyes in the respective layers; and
(d) methods of using an emission layer containing an emitting dye and a carrier transport layer adjacent to the emission layer and containing an emissive dopant, and from the excitons generated by carrier recombination in the emission layer, a portion of the excitation energy is moved to the emissive dopant, and the emissive dopant is caused to emit light (see Japanese Patent Application Laid-open No. 2002-93583 and Japanese Patent Application Laid-open No. 2003-86380).
However, the above-described multicolor-emission organic EL devices rely on either simultaneous excitation of a plurality of types of emissive materials, or on movement of energy between a plurality of types of emissive materials. It has been reported that in such devices, the balance of emission intensities among emissive materials changes with the passage of time during driving or with the current passed, and that there are concerns that the hues obtained may change.
As other methods of obtaining a multicolor-emission organic EL device, Japanese Patent Application Laid-open No. 2002-75643, Japanese Patent Application Laid-open No. 2003-217859 and Japanese Patent Application Laid-open No. 2000-230172 propose color conversion methods in which a monochromatic-emission organic EL device and a color conversion film are used. The color conversion film used is a layer containing one, or a plurality of color conversion materials which absorb short-wavelength light and convert the light to longer wavelengths. As methods of formation of color conversion films, application of an application liquid in which color conversion material is dispersed in a resin, and use of dry processes such as evaporation deposition or sputtering to deposit color conversion materials, are being studied.
However, as the concentration of the color conversion material in a color conversion film rises, a phenomenon called concentration quenching occurs, in which the absorbed energy repeatedly moves between the same molecules without resulting in emission, and deactivation occurs. In order to suppress this phenomenon, the color conversion material is dissolved or dispersed in some medium to lower the concentration, as described in Japanese Patent Application Laid-open No. 2000-230172 and elsewhere.
Here, if the concentration of the color conversion material is lowered, the absorbance of the light to be absorbed is reduced, and adequate converted light intensity cannot be obtained. To address this problem, the color conversion film is made thick, the absorbance is increased, and color conversion efficiency is maintained. When using such a thick color conversion film (film thickness approximately 10 μm), such problems as disconnection of electrode patterns at step portions, difficulty in increasing definition, and residual water or solvent in the film (when combined with an organic EL device, residual water or solvent causes alteration of the organic EL layer, resulting in display faults) exist. On the other hand, from the standpoint of reducing viewing angle dependence, there is also a conflicting demand for a thinner color conversion film.
In order to provide a color conversion film which can maintain adequate converted light intensity, use of a method of evaporation deposition of a host-guest system color conversion film having a film thickness of 2 μm or less is being studied in Japanese Patent Application Laid-open No. 2007-157550. However, when forming a color conversion film using an evaporation deposition method, if the film is formed over the entirety of the display face, division into three primary colors to cause emission is not possible, and so some means for forming a fine pattern corresponding to specific pixels becomes necessary.
At present, as a method of forming a pattern in a thin film of evaporation-deposited material, methods of selective application using a metal mask have long been used. However, due to limits on the mask material and thickness, the fineness of the pattern of the metal mask used has a limit of a definition level of 150 ppi. Application of selective application methods using metal masks to patterns with definitions higher than this entail such problems as increased difficulty, extreme difficulty when increasing the area, and reduced yields.
As a method of patterning a thick-film color conversion layer, Japanese Patent Application Laid-open No. 2006-32021 studies a method in which a relief pattern is formed on a supporting substrate, color conversion material is applied to the relief pattern portion, causing the depressed portions to be buried by the color conversion material, and then the color conversion layer is polished to planarize the surface and perform patterning. However, in the above method, there are the problems that the efficiency of material utilization of expensive color conversion material is poor, and moreover that the color conversion performance is degraded by direct polishing of the color conversion layer.
Further, Japanese Patent Application Laid-open No. 2000-353594 proposes a method in which barrier walls are formed in the vicinity of pixels on a substrate, and an inkjet method is used to selectively apply phosphor material between barrier walls to perform patterning. When performing patterning of a color conversion film using this method, because a dilute solution of color conversion material is used in the inkjet method, the need arises to make the height of the barrier walls approximately 10 times higher than the film thickness required for the color conversion material, in order to prevent flowing into adjacent pixels during dispensing. As a consequence, even in cases when (a) bonding with a separately manufactured organic EL device substrate, or (b) a planarization layer is provided on the color conversion layer, and an organic EL device is formed thereupon, a gap occurs between the color conversion layer and the organic EL device equal to the height of the barrier walls and the film thickness of the planarization layer. This gap causes the problems of crosstalk phenomena in which light from the EL device leaks into adjacent pixels, and of the phenomenon of losses due to inadequate incidence of light from the EL device onto the color conversion layer.
Recently, as means for resolving these problems, Japanese Patent Application Laid-open No. 2006-32010 has proposed an organic EL display structure in which a color filter and color conversion layer are formed, directly on the upper transparent electrode of a top-emission structure organic EL device in which an organic emission layer is sandwiched between a cathode and an anode on a substrate, and light with three primary colors is emitted. This method has advantages for increasing definition, but because low-molecular-weight organic EL material is presented as an example of the emission layer, the annealing temperature during formation of the color filter and color conversion layer is limited to 100° C. or lower. Consequently it is difficult to adequately remove from the color filter and color conversion layer the moisture and solvents which exert the most adverse effects on the organic EL material, and these can easily be imagined to critically degrade the device lifetime.